Aromatic hydrocarbon (wherein benzene, methylbenzene and dimethylbenzene (i.e. xylene) are referred to be B, T and X respectively and they are jointly called as BTX) is an important basic organic chemical material. Around 90% of aromatic hydrocarbons all over the world comes from the catalytic reforming process of petroleum as raw material and from the gasoline as a byproduct from the steam cracking. Only 10% of the total yield of aromatic hydrocarbons comes from the coal route. With the increasing depletion of petroleum resources and thus the high price thereof, the energy and chemical industry with mainly a petroleum route faces unprecedented serious challenges.
With the development of natural gas and shale gas in North America and Middle East, a large amount of light hydrocarbons are produced as a byproduct. The light hydrocarbon produced by shale gas as byproduct replaces a part of naphtha for steam cracking, and thus a trend of conversion to a light fraction appears in the raw material for steam cracking. In the future, a reduction trend may be seen in the yield of aromatic hydrocarbons from steam cracking byproducts, which results in a shortage trend of the yield of aromatic hydrocarbons all over the world in the future. Thus, the development of a new technology using an oxygenate including methanol as raw material for a partial substitute of the production of aromatic hydrocarbon with petroleum has a great potential.
U.S. Pat. No. 3,931,731 reported a method for the production of gasoline with methanol as raw material. Although a considerable number of aromatic hydrocarbons are present in gasoline, the process takes the production of gasoline liquid fuel with a high octane number as a main target and the product further contains a large amount of isoparaffin components having high octane numbers. Thus, the technology of producing gasoline with oxygenate(s) as raw material(s) has a technical problem of a low total yield of aromatic hydrocarbons.
Chinese patent CN101244969B reported a C1-C12 hydrocarbons or a methanol aromatization and catalyst regeneration device. The method does not relate to the conversion of non-hydrocarbons in the reaction product, specific reaction or separation procedures. The added value of non-hydrocarbons in the product is relatively low. Moreover, the production of a large mount of non-hydrocarbons in the product will reduce the efficiency of aromatization of raw material and increase the cost during aromatization.
Chinese patent CN101671226 reported conducting aromatization reaction in an aromatization reactor with a mixture of methanol and one or more of C1-C12 hydrocarbons. The method only takes into consideration of a one-time conversion of methanol and C1-C12 hydrocarbons and does not relate to a cycle conversion of non-hydrocarbons to aromatic hydrocarbons in the reaction product. Thus, the process has a problem of a low yield of aromatic hydrocarbon. The research shows that the reaction temperature of methane aromatization is up to 700° C., but the conversion rate of methane is less than 20% and the yield of aromatic hydrocarbons is only around 10%. The highest reaction temperature of aromatization in the process is only 650° C. Thus, if the components of C1-C12 hydrocarbons contain methane of lower activity, the presence of methane or the accumulation thereof in cycle flow may reduce the utilization efficiency of the reactor.
Chinese patent CN101820919B reported a procedure of producing a dimethylbenzene product with methanol or an oxygenate. In the procedure, B and T in the liquid phase aromatic hydrocarbon product are separated one by one, as well as non-aromatic hydrocarbons having more than 6 carbon numbers are also separated. In the aromatic hydrocarbon mixture, non-aromatic hydrocarbons and aromatic hydrocarbons with the same number of carbon atoms have extremely close boiling points and it is very difficult to separate them. The current technique of separating aromatic hydrocarbon usually achieves the separation of non-aromatic hydrocarbons from aromatic hydrocarbons by a manner of solvent extraction of a mixed hydrocarbons flow containing benzene, methylbenzene and dimethylbenzene light aromatic hydrocarbon and then separates benzene, methylbenzene, dimethylbenzene and C9+ aromatic hydrocarbon one by one. In the procedure disclosed in Chinese patent CN101820919B, non-aromatic hydrocarbons having no more than 6 carbon numbers are subjected to a cycle conversion to aromatic hydrocarbon. However, non-aromatic hydrocarbons having more than 6 carbon numbers are not subjected to a cycle conversion to aromatic hydrocarbon. Thus, a problem of a low aromatic hydrocarbon yield is present during the process. As compared to the direction utilization of a hydrocarbons mixture containing B and T, the energy consumption during the separation process of liquid phase aromatic hydrocarbon from non-aromatic hydrocarbon in Chinese patent CN101820919B will be higher. Moreover, in said procedure, simply only H2 and CH4 are removed from the gas phase components thereof. Oxygenates such as CO, CO2, formaldehyde, formic acid and acetic acid are produced inevitably during the process of producing aromatic hydrocarbon with oxygenates. These components cannot be further converted to aromatic hydrocarbon. Without removal, they will be accumulated in the reaction system and thus affect the efficiency of the reactor.
Chinese patent CN101607864B reported a method of increasing the yield of dimethylbenzene by adding benzene or methylbenzene to the aromatization system of oxygenate. In the product of producing aromatic hydrocarbon with oxygenate, there are a large amount of non-aromatic hydrocarbons, unconverted oxygenates and intermediate product of oxygenate in addition to aromatic hydrocarbon products. Theses non-aromatic hydrocarbon products have a large amount of components. If Separating them or selling them as mixture, their added values are relatively low. By adding benzene or methylbenzene components from the reaction products or from outside to the aromatization process, the yield of dimethylbenzene product may be increased via the alkylation of methanol. However, the method requires relatively high energy consumption for separating benzene and methylbenzene respectively, which will necessarily increase the production cost of aromatic hydrocarbon. In addition, the aromatization catalyst used in the method uses a molecular sieve catalyst upon silanization and metal modification. Although the silanization modification will improve the shape selectivity of the catalyst to a certain degree, it will cause the blockage of pores and reduction of catalyst activity.
Chinese patent application CN1880288A reported a process of methanol conversion for preparing aromatic hydrocarbons and catalyst. In the technique of preparing aromatic hydrocarbons with methanol disclosed by the above patent, two fixed-bed reactors in series are used; after the reactant, methanol, enters the first section of the reactor for reaction, the first section of the gas phase product continues to enter the second section of reactor for reaction, aromatic hydrocarbon and non-aromatic hydrocarbon are obtained upon separation of the first and second sections of liquid phase products. The process of producing aromatic hydrocarbons with oxygenates is a process of strong exothermicity and relatively rapid deactivation due to carbon deposition. The fixed-bed reactor has a difficulty of heat transfer and heat removal and has a problem of being difficult to control the temperature stably. In the process, only the gas phase components in the byproducts of the first reactor are used for aromatization thereof for conversation to aromatic hydrocarbons. The non-aromatic hydrocarbons as the byproducts in the second reactor are not further subjected to cycle conversion to aromatic hydrocarbon. Thus, the process has a technical problem of a low total yield of aromatic hydrocarbon.
U.S. patent application US20100185033A1, reported a method of producing aromatic hydrocarbons with aliphatic alcohols having carbon numbers between 1 and 10 as raw material. The catalyst is a molecular sieve catalyst loaded with 0.0001 to 20% of La and 0.0001-20% of M metal, wherein M is selected from at leas one of molybdenum (Mo), cerium (Ce), or caesium (Cs) and the zeolite is selected from ZSM-5, ZSM-11, ZSM-23, ZSM-48 and ZSM-57. The reaction process conditions are a temperature of 250 to 750° C., a pressure of 0 to 3 MPa, a raw material space velocity of 0.1 to 500 h−1. The method does not relate to a step of producing aromatic hydrocarbon by a further cycle conversion of a byproduct, non-aromatic hydrocarbons. Thus, the process has a problem of a low total yield of aromatic hydrocarbons.
U.S. Pat. No. 6,489,528B2 reported a method of producing aromatic hydrocarbon with methanol or dimethyl ether as raw material and two types of molecular sieve catalysts, wherein one of them is a silicoaluminophosphate molecular sieve and another one is a ZSM-5 molecular sieve catalyst which contains a metal Zn and an element from Group IIIA or Group VIB. The method does not mention specific reaction and separation procedures and there is no further utilization solution of non-aromatic hydrocarbon components in the product.
In addition to aromatic hydrocarbon products, there are a large amount of non-aromatic hydrocarbon hydrocarbons components, a small amount of unconverted oxygenate materials and other intermediate oxygenate components as byproducts in the products from the production of aromatic hydrocarbons with oxygenates. These components are very complicated. The economy of using them alone upon separation is poor. As fuel gas, their added values are also very low. If such part of components can be converted to aromatic hydrocarbons, a total yield of aromatic hydrocarbons in the production of aromatic hydrocarbons with oxygenates can be notably improved, the production cost of aromatic hydrocarbons can be reduced and a notable economic benefit is produced.
In the components of aromatic hydrocarbons, a light aromatic hydrocarbon—BTX is an aromatic hydrocarbon product having the most wide value and use. In the aromatic hydrocarbon components, dimethylbenzene is a product having a relatively wide use and a relatively high added value. In the aromatic hydrocarbon products, the paths for using methylbenzene directly are very limited. Its main use is converting methylbenzene to dimethylbenzene product which is in great demand and has a relatively high added value through selective disproportionation of methylbenzene or a transalkylation process with a C9 component.
Introducing non-metal oxides and metal oxides, especially non-metal oxides, for modification is reported in the prior art. However, the presence of these components may cause a blockage of molecular sieve pores, a failure to achieve the optimum modification effect and a reduction of aromatization yield of catalyst.
To sum up, the technical problem of a low total yield of aromatic hydrocarbons and a high energy consumption si present during the process of producing aromatic hydrocarbons with oxygenates as raw material in the prior art.